Torque tubes are typically used for mechanically transmitting torque from power drive unit to a rotating device that provides translation motion. For example, a torque tube is commonly used in a ground-based vehicle to transfer torque from an engine to a front or rear axle, which in turn rotated wheels of the vehicle providing propulsion. Another example is in an aircraft whereby a torque tube may be utilized for transmitting torque between a power drive unit and a ballscrew, which is providing either horizontal or vertical translation of airfoil surface adjusting devices such as flaps and slats.
Many applications of torque tubes, including the above mentioned, require that the torque tube be lightweight, inexpensive, have high fatigue strength, and an ultimate yield strength at an end fitting equal to or exceeding that of the tube itself. Thus, torque tubes for aircraft are formed from 2024 aluminum due to its inherent lightweight and strength characteristics over that of steel.
A typical torque tube has an elongated tube section, which is conformed over a fitting. The fitting has multiple chamfered surfaces between a pair of upper flat surfaces and multiple lower flat surfaces with chamfer angles that are approximately 45 relative to the lower surfaces. The upper surfaces transition to the chamfer surfaces at relatively sharp chamfer edges. The fitting also has multiple overflow groves that transition between recessed areas and the lower flat surfaces, via groove edges.
The chamfer edges and the groove edges cause notches to be formed in the elongated tube, when being conformed over the fitting. Thinning occurs in the elongated tube near the notches and can cause fatigue cracking over time. Cracking, as known in the art, reduces fatigue life of a component and is therefore undesirable.
Elongated tubes are normally procured having a T-3 temper condition. The elongated tubes are treated with a chemical film such as alodine to create a corrosive inhibiting surface coating. The elongated tubes are heat treated for an extended period of time in a furnace such that the elongated tubes are of a solid solution or in a W tempered condition. A disadvantage with heat treating the elongated tubes is that the corrosive inhibiting surface coating is negatively affected during the heat treatment. The elongated tubes are placed in a freezer, to maintain the W condition and prevent aging of the tubes, up until electromagnetic forming over the end fittings.
During forming of the elongated tubes, tube walls are significantly thinned. Due to stretching and thinning of the tube walls, the tubes are weakened and are susceptible to cracking under fatigue. Thinning can be difficult to detect by ordinary inspection procedures without destructive testing.
Upon completion of forming the elongated tubes, depending upon length of the tubes, the tubes are hand straightened. The elongated tubes are then naturally aged to a T-42 temper until a significant amount of tubes are ready for artificial aging, due to costs of operating a furnace as to perform artificial aging. The elongated tubes are artificially aged in a furnace to again alter temper of the tubes from having a T-42 temper to having a T-62 temper, which is of strength suitable for application use.
The above-mentioned process of manufacturing a torque tube is time consuming and costly due the amount of steps within the process and the requirements for each step.
It is therefore, desirable to provide a method of manufacturing a torque tube that provides a more durable chamfer portions with increased fatigue life, minimizes warping of the elongated tubes, and has decreased production cycle times and manufacturing costs. It is also desirable that the manufacturing method provides a torque tube having an elongated tube with at least the same temper of current elongated tubes.